1. Field of the Invention
The invention relates to a self-adhesive lidding film for packaging electronic components and to the use of packages lidded in this way, in particular in high-speed automatic machines.
2. Description of the Prior Art
Electronic components, in particular micro-electronic components, are packaged in thermoformed caverns of thermoplastic sheeting, such as, for example, in sheeting made from polyvinyl chloride (PVC), polystyrene (PS) or polycarbonate (PC), these plastics being processed either in pure form or filled with carbon black. These so-called belts have for many years been sealed with lidding films by means of hot-melt adhesives and processed in automatic machines, i.e. opened and the components packaged in them removed.
However, there are also already self-adhesive lidding films for such applications whose adhesive layer has been deactivated in the centre by means of a conductive or nonconductive plastic film. This deactivating strip covers the openings of the support belt so that the components do not come into contact with the self-adhesive layer. The adhesive strips with widths of 0.5 to 1.2 mm remaining at the two edges of the sealing sheet bond the latter to the support belt. A sufficient adhesive force here is regarded as being a peel-off force of the sealing sheet from the support belt in the range 20-100 cN.
Lidding films of this type have been described in the prior art and are also commercially available, for example as "cover tape YR 2666" from 3M. In addition, products of this type are described in Siemens Patent EP 51 168, and also in DE-A 39 28 712, DE-A 39 28 713 and EP-A 300 838.
However, the products of the prior art have disadvantages which are particularly noticeable in practice. For example, packages of this type containing electronic components are employed in high-speed automatic machines in which the slightest disturbances or unevenness has consequences for the entire process in which the use of a package lidded in this way has been integrated. Thus, for example, lidding films which adhere nonuniformly can result in problems as a consequence of differing polarities of the various materials employed, and the lidding film must therefore adhere equally well to various packaging belts, and must do so immediately and with sufficient strength. In addition, peeling-off of the lidding film in a high-speed automatic machine of this type must not, for example, result in adhesive residues on the packaging belt, since such residues can build up and accumulate, although perhaps only in very small amounts at individual point, but in the overall process giving interfering amounts at individual machine parts and then interfere with the process. Any residue of adhesive compositions must therefore be avoided, in particular after exposure of the lidded package to moisture and heat, as required by many belt processors, for example in the IEC 68-2-3 tropics test.
The object of the invention was to provide a remedy here and to avoid the disadvantages of products of the prior art, but at least to reduce them to an extent acceptable for industry.